[CMake] Update to requiring CMake 3.4.3

Summary:
This is as per the discussions on developer lists:

http://lists.llvm.org/pipermail/llvm-dev/2016-April/098780.html
http://lists.llvm.org/pipermail/llvm-dev/2016-May/100058.html

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20828

llvm-svn: 271329
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 3e0815c..992caa6 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -3,7 +3,7 @@
 #===============================================================================
 # Setup Project
 #===============================================================================
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.4.3)
 
 if(POLICY CMP0042)
   cmake_policy(SET CMP0042 NEW) # Set MACOSX_RPATH=YES by default